Engineering plastics have distinguished characteristics such as a high mechanical strength, a high creep resistance, etc. and thus are widely used in various fields as a substitute for metals. Even in the fields of industrial rubber products and automobile vibration-absorbing rubber products, formation of rubber-resin composite materials based on resins has been now in progress.
Conventional processes for producing rubber-resin composite materials such as rubber-bushed plastic rods, bushes, engine mounts, etc. include a process, which comprises applying a rubber-based adhesive to resin moldings, followed by vulcanization bonding to an unvulcanized rubber, but the process suffers from such problems as occurrence of deformation or physical property degradation of the resin moldings due to the mold-inside heat, a prolonged time for elevating the temperature of resin moldings up to a necessary temperature for the vulcanization and an inevitable production cost increase due to a longer time than that required for the vulcanization of metal-rubber.
As one of the processes applicable to production of the aforementioned bushed plastic rods, a process, which comprises providing a vulcanized rubber molding in a mold, followed by injection molding a molten resin into the mold (JP-B-7-55510), where the desired surface of the vulcanized rubber molding for bonding to the resin is subjected to a treatment according to a method (1) comprising a chlorination and application of a vulcanizable adhesive containing a resol type phenol resin and an aldehyde-modified polyvinyl alcohol as the main components or according to a method (2) comprising application of a vulcanizable adhesive containing chlorosulfonated polyethylene as the main component.
The above-mentioned method (1) suffers not only from diffusion of an organic solvent used in the chlorination into the atmosphere and an influence on workers or a cost increase in fire-preventive facility, etc. due to the use of the organic solvent, but also from a fear of development of crack generation-starting points when a shearing force is applied to the chlorinated vulcanized rubber molding itself. The method (2) requires a heat treatment (prebaking) of the adhesive-applied vulcanized rubber molding in advance to the injection of the molten resin into the mold and also requires a heat treatment of the vulcanized-resin composite material after the injection. No stable quality bonding can be obtained unless such a heat treatment is carried out fully.